The +Pack is for those that already own a Glif, but want the Serif and Ligature add-ons. It's the "+" part in Glif+.

The Serif is designed to keep your iPhone incredibly secure on the tripod. While the Glif is great for normal use, the Serif will keep your phone safe in more extreme situations. And, when you are not using the Serif, it fits snuggly inside the Glif, making it very compact.

Additionally, the +Pack comes with the Ligature, a simple keyring loop that attaches to the tripod thread on the Glif. Now, you'll have a way to always keep your Glif handy, by attaching it to your keychain, backpack, purse, or anything, really.